Machine for making a heat exchanger tube

ABSTRACT

Apparatus for forming spine-finned heat exchanger tubing is disclosed in which a strip of metal is slit at a first cutting station to provide intermediate spines having a width along the length of the strip equal to twice the desired spine width. The intermediate spines are then cut in half at a second cutting station. The apparatus for slitting the strip utilizes a main cutter roll in combination with two or more cutter rolls located at peripherally spaced locations. The depth of cut of alternate spines is varied to improve strength and heat flow characteristics. The tube is wound so that pairs of spines are axially offset from each other and peripherally diverging from the adjacent spine of an adjacent pair.

United States Patent Venables, III

MACHINE FOR MAKING A HEAT EXCHANGER TUBE Appl. No.: 135,183

Inventor:

Assignee:

US. Cl. ..29/202 D Int. Cl. 1323 15/16 References Cited UNITED STATES PATENTS Wade ..29/157.3 AH Venables..... .....29/l57.3 AH Venables..... .29/l57.3 AH

Venables ..29/202 D Mar. 27, 1973 3,362,058 l/l968 Morris et al. ..29/157.3 AH 3,550,235 12/1970 Jarvis et a1. ..29/l57.3 AH 3,557,427 1/ 1971 Pignal v.29/202 D Primary Examiner-Thomas H. Eager Att0meyMcNenny, Farrington, Pearne & Gordon ABSTRACT Apparatus for forming spine-finned heat exchanger tubing is disclosed in which a strip of metal is slit at a first cutting station to provide intermediate spines having a width along the length of the strip equal to twice the desired spine width. The intermediate spines are then cut in half at a second cutting station. The apparatus for slitting the strip utilizes a main cutter roll in combination with two or more cutter rolls located at peripherally spaced locations. The depth of cut of alternate spines is varied to improve strength and heat flow characteristics. The tube is wound so that pairs of spines are axially offset from each other and peripherally diverging from the adjacent spine of an adjacent pair.

6 Claims, 7 Drawing Figures MACHINE FOR MAKING A HEAT EXCHANGER TUBE BACKGROUND OF THE INVENTION This invention relates to a novel and improved spinefinned heat exchanger tube and to a method and apparatus for making same.

PRIOR ART In my prior U.S. Pats., Nos. 3,005,253 dated Oct. 24, 196i; 3,134,166 dated May 26, 1964; and in my pending application, Ser. No. 54,304, filed July 13, 1970, US. Pat. No. 3,688,375 I disclose a heat exchanger tube structure in which a spine fin is helically wound around a base tube to provide a lightweight, highly efficient heat exchange structure. The spines of such heat exchanger tubes are formed by slitting an elongated strip of metal, such as aluminum, from one or both sides to form separate tongue like spines attached to the strip at their inner ends. After the strips are cut, they are formed so that the spines extend substantially at right angles from the strip base and the strip is then wound around a tube in a helical manner. In my pending application, supra, an improved tube and method and apparatus for forming such tube involves the simultaneous forming and winding of two or more strips. In such a machine, higher outputs are obtained and a tube is produced having improved thermal characteristics.

Normally, the spines are cut in the strip by cooperating ratchet type cutter rolls having interengaging sawtoothed shaped cutting teeth. There are practical limitations in the manufacture of such cutting rolls which require a minimum spacing between the cutting teeth. Further, there is a tendency in such cutting operation to tear or rupture the strip material where the spines join the base strip, and if the width of the spines in the direction of the strip are too small, the connection of the spines to the base strip are weakened to a point where they are unsatisfactory. Consequently, it has been impractical in the past to reduce the width of the spines in the direction of the strip to less than twenty-five thousandths of an inch. Because of this, it has been impractical in the past to manufacture spined strips of lesser width in the direction of the strip so as to obtain even higher heat exchange efficiencies which could otherwise be obtained.

SUMMARY OF THE INVENTION With the present invention it is possible to overcome the practical limitations which have existed in the past in reducing the width of spines in the direction of the strip so as to improve the heat exchange efficiency of tubing incorporating such spined strips. Further, such reduction in width is obtained without objectionable weakening of the connection of the spines to the base material.

In the illustrated embodiments, a strip of material is first passed through a first cutting station in which the material is slit from at least one edge at substantially uniform intervals. The strip is subsequently passed through a second cutting station wherein intermediate slits are cut in the spines formed in the first cutting operation. Because two separate cutting operations are performed, it is not necessary to reduce the size of the cutting teeth on the rolls to a size which would render their manufacture and maintenance excessively difficult. Consequently, the rolls required in accordance with this invention have cutting teeth sufficiently large to facilitate ease in manufacture and maintenance. Further, the length of the cut or slit in the first cutting operation is different from the length of the cut or slit in the second cutting operation. Consequently, the tearing or rupturing at the base of the spine occurring in the first cutting operation is offset from the tearing or rupturing of the material at the base of the cut in the second operation so that they do not mutually cooperate to weaken the spine material at its base.

In accordance with another aspect of this invention, alternate slits are formed to laterally offset the adjacent edges of the spines so as to interrupt the flow of fluid over the spines and improve the heat exchange capacity of the tube. The edges of the intermediate spines which are more nearly coplanar are spread during the wrapping operation, so again flow over the spines is interrupted and improved heat exchange efficiency is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partially in longitudinal section, of a spine-finned heat exchanger tube in accordance with this invention with only two turns of spine strip shown to simplify the illustration;

FIG. 2 is a plan view of a piece of strip material after it has been slit but before it is formed and wrapped;

FIG. 2a is an enlarged edge view of the strip illustrated in FIG. 2',

FIG. 3 is a schematic plan view of a slitting apparatus for forming the strip of FIG. 2;

FIG. 3a is an enlarged view (not to scale) illustrating the manner in which the cutting apparatus functions;

FIG. 3b is a side elevation of the cutting rolls illustrated in FIG. 3a; and

FIG. 4 is a schematic plan view similar to FIG. 3 but illustrating an embodiment in which the cutting apparatus is arranged to simultaneously slit two strips which are subsequently formed and wrapped simultaneously on a tube in a double helix.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an improved spine-finned tube in accordance with this invention. The tube includes a base tube 10 usually formed of copper or aluminum and a spined fin strip 11 helically wound around the tube 10. The illustrated strip 11 is generally U-shaped and includes a base section 12, inturned hem sections 13, and radially extending spines 14. The two legs of the U are each formed with similar spines so only the spines of a single leg need be discussed in detail with the understanding that it applies equally to the spines of the other leg.

The spines of each leg may be considered as a series of pairs of spines with each pair designated by the letter A. Each pair of spines includes a first spine 16 and a second spine 17 separated by an intermediate slit l8 and adjacent pairs of spines are separated by a primary slit 19. The primary slits 19 extend toward the base tube 10 a greater distance than the intermediate slits 18. Consequently, the spines 16 of one pair diverge from the spines 17 of an adjacent pair in a peripheral direction due to the winding of the strips on the tube at a greater angle than the divergence between the adjacent spines of each pair. However, as discussed more fully below, the spines 16 and the spines 17 of each pair of spines A diverge in an axial direction even though they do not diverge in a substantial amount in a peripheral direction around the tube. Because each of the spines diverge a substantial amount in either a peripheral direction or an axial direction with respect to the adjacent spines, the flow of air over the spines is interrupted by the edges of each spine, and extremely efficient heat exchange is accomplished. Such interrupted flow prevents any substantial development of a surface boundary layer which would inhibit efficient heat exchange. Further, since alternate slits vary in depth, the tearing or rupturing of the material which tends to occur at the bottom of each slit as illustrated at 21 is radially spaced from the tearing or rupturing of the material at an adjacent slit. Consequently, such tearing at 21 does not cooperate with the tearing at an adjacent slit to weaken the connection of each spine and the adjacent base portion or to inhibit flow of heat between the base portion 12 and the individual spines.

Referring to FIGS. 2 through 4, FIGS. 2 and 2a illustrate the forming of a spine-finned strip before it is formed to the hemmed U-shape and before it is wrapped around the tube. Such strip is slit by an apparatus illustrated in FIGS. 3, 3a, and 3b. Such apparatus first cuts the primary slits 19 in an elongated strip, as illustrated in the left portion of FIG. 2, with slits 19 extending inwardly from opposite edges toward the center portion of the strip. After the first cutting operation,intermediate spines 25 are provided which have a width, along the length of the strip, twice the desired width of the final spines 16 and 17. The inner ends of the slits 19 are spaced apart by a distance B necessary to allow the forming of the base 12, the hems l3 and preferably a sufficient additional spacing to cause the inner ends of the primary slits 19 to terminate at a location radially spaced slightly from the hems 13 as illustrated in FIG. 1.

After the primary slits 19 are formed in the strip, the strip is again cut to form the intermediate slits 18. In the illustrated embodiment, the intermediate slits 18 are located half-way between the primary slits 19 so that the final spines 16 and 17 are substantially equal in width in the direction of the strip. During the slitting operations, each of the spines 16 and 17 of each pair of spines A are laterally offset from each other as best illustrated in FIG. 2a, and each spin 16 is substantially coplanar with the adjacent spine 17 of an adjacent pair. A slight lateral offset does exist between such spines, but it is much less than the offset between the adjacent spines of the pairs of spines.

The intermediate slits 18 extend inwardly from opposite edges of the strip and terminate at inner ends which are spaced further apart than the slits 19. Consequently, the tearing 21 at the inner ends of the primary slits 19 are inwardly spaced from the tearing 21 at the inner ends of the intermediate slits 18. Consequently, the tearing on one side of a given spine is radially spaced in the final strip from the tearing on the opposite side, and the two tear portions do not cooperate to weaken the junction between the slits and the base portion of the strip and do not provide an excessive barrier for heat flow between the base and the spines.

The strips are slit preferably by a structure as illustrated in FIGS. 3, 3a and 3b. The slitting structure includes a center cutting roll 26 which is driven for rotation in an anticlockwise direction about its center axis 27 and a pair of idler or driven rolls 28 and 29 which rotate about their axes 31 and 32, respectively. The two rolls 26 and 28 cooperate to form a first cutting station 33, and the two rolls 26 and 29 cooperate to form a second cutting station 34.

As best illustrated in FIG. 3b, each of the roll cutters 26, 28, and 29 are formed with axially spaced sawtoothed shaped cutting teeth 26a and 26b, 28a and 28b, and 29a and 29b which intermesh at the two cutting stations 33 and 34 to form the slits 18 and 19 in a strip of material 36. The spacing of the teeth is equal to the distance between the slits l9'which, of course, is also equal to the distance between the slits 18. The teeth 26a and 26b on the roll 26 and the teeth 28a and 28b on the roll 28 are axially spaced by a distance equal to B so that they cut the slits 19 to the depth required and leave uncut the center portion of the width B in the strip.

After the strip 36 feeds through the cutting station 33, it is provided with the slits 19, intermediate the spines 25, and is an intermediate strip 37. The strip 37 passes from the cutting station 33 over an idler roll 38 spaced so that the strip feeds directly into the cutting station 34. The idler roll 38 is mounted on an eccentric 39 so that its position can be adjusted accurately to position the intermediate strip 37 for proper location of the intermediate slits 18. The spaced cutting teeth 29a and 29b on the roll 29 have an axial length less than the cutting teeth on the rolls 26 and 28 and are axially spaced by a distance corresponding to the spacing between the slits 18. Therefore, the slits 18 do not extend toward the center of the strip through the same distance as the slits 19.

FIG. 3a illustrates in enlarged scale, the cutting action which occurs at the two cutting stations 33 and 34. As the strip 36 passes through the cutting station 33, the two rolls 26 and 28 form the intermediate spines 25 having a width along the length of the strip which is equal to twice the final width of the spines 16 and 17. In the process of the cutting, the intermediate spines 25 are bent to a diagonal position as illustrated in FIG. 3a and the adjacent edges are laterally offset from each other.

After the intermediate strip 37 passes around the idler roll 38, it enters the second cutting station 34, and each intermediate spine 25 is cut along its center to form the spines 16 and 17. During this operation, the spines l6 and 17 of a pair A, which has previously existed as a single intermediate spine 25, are laterally offset from each other, but the spine 16 of one pair is bent back into substantially a coplanar relationship with the spine 17 of an adjacent pair. The strip 42 is completed insofar as the slitting operations are concerned after it leaves the second cutting station 34.

When the cutter teeth on the rolls are formed so that they are parallel to the respective roll axes, the adjacent edges of the spine of each pair of spines tend to be somewhat parallel and laterally offset with respect to each other. When greater lateral offset is desired between such adjacent edges, the teeth 29a and 29b on the roll 29 may be formed with a slight conical shape so that they engage and cut the strip first adjacent to the edges of the strip and progressively out toward the center. When the teeth 29a and 2% are slightly conical, the teeth on the rolls 26 and 28 may remain parallel to their axes. Such increase in lateral offset obtained by using slightly conical teeth increases the axial displacement between the spines of the pair of spines on the final tube.

In most instances, proper cutting occurs between the rolls 26 and 28 even when the teeth alone are utilized to drive the roll 28. However, in the secondary cutting between the rolls 26 and 29 at the second cutting station 34, there is a tendency in some instances for the intermediate spine to turn or twist and cause the roll 29 to move ahead of proper tooth registration. When this occurs, clean cutting is not obtained. When such a problem exists, it is preferable to provide a positive drive between the rolls 26 and 29 to maintain proper registry of their teeth. Such a positive drive may be provided by forming the rolls 26 and 29 with integral gear teeth axially on one or the other side of the cutting teeth which intermesh to maintain proper cutting tooth registration.

Subsequently, the strip is passed through a preliminary forming operation as illustrated in my copending application, supra, a hemming operation of the type also illustrated in such pending application, and is i then wound on the base tube in a helical manner. In the embodiment of FIGS. 3, 3a, and 3b, a single strip is cut or slit by the cutting rolls so that the tube would normally be wound as a single helix with a single strip rather than as a double helix with a double strip as illustrated in such copending application. In some instances where even narrower spines are desired, it is possible that the strip can be passed through three cutting stations and the idler rolls suitably adjusted so that the intermediate spines 41 are cut into more than two final spines.

I FIG. 4 illustrates an embodiment which is particularly adapted for use in a machine of the general type illustrated in my copending. application, supra. In this embodiment, two strips 51 and 52 are simultaneously cut. A center-driven cutter roll 53 rotates about its center axis 54 and intermeshes with four cutter rolls 56, 57, 58, and 59 each of which rotates about its respective axis and each of which is formed with cutter teeth which mesh with the center roll at four locations around the center roll 53. Preferably, the rolls 56 and 58 are diametrically opposite each other as are the rolls 57 and 59. The four rolls cooperate with the center roll 53 to define four cutting stations 61, 62, 63, and 64. An idler roll 66 is associated with the two cutter stations 61 and 62 and an idler roll 67 is associated with the two cutter stations 63 and 64.

The strip 51 first passes through the cutting station 61 wherein the primary slits 19 are formed to provide the intermediate spines of the type illustrated as 25 in the first embodiment. The intermediate strip 68 passes from the cutting station 61 over the idler roll 67 and is then fed back between the cutter rolls at the cutting station 62. Here again, the idler roll 66 is preferably supported on an eccentric so that its location can be accurately adjusted so that the intermediate slits are formed in the middle of the intermediate spines. The

strip 69, after it passes through the cutting station 62, is subsequently formed to the desired shape and wound on a base tube. Examples of the apparatus for forming and winding the strip are illustrated in my prior patents listed above and such patents are incorporated herein by reference. Here again, the teeth on the roll 57 are sized so that the length of the intermediate slits is less than the length of the primary slits.

A similar operation simultaneously occurs on the strip 52. The strip is first passed through the cutting station 63 to form the primary slits 19. After these slits are formed, the strip passes over the idler roll 67 and into the cutting station 64 which forms the intermediate slits. After slitting the strip 71 is formed and wound on the base tube. In this embodiment where two strips are simultaneously slit and formed, the two strips are sim ultaneously wound on a single base tube 10 in a double helix as illustrated in my copending application, supra.

With the present invention, a spine-finned tube is provided which has improved heat transfer efficiency, because the spines are arranged to prevent or minimize the occurrence of boundary layers and because nar rower fins are possible. The heat exchange capacity is further improved since the narrower spines provide greater surface area when compared to the wider spines previously manufactured. Further, in accordance with the method and apparatus of this invention, very narrow fins can be formed without necessitating the manufacture of cutter rolls with very closely spaced teeth. Consequently, the cutter rolls can be manufactured and maintained with economy even though the width of the final spines in the direction of the strip is extremely short in the order of 12.5 to fifteen thousandths of an inch. Further, the formation of alternate cuts with different depths-eliminates excessive weakening which would otherwise occur at the inner ends of the spines.

Although preferred embodiments of this invention are illustrated, it should be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention disclosed and claimed herein.

What is claimed is:

l. A machine for forming spine fins for heat exchanger tubing or the like comprising first cutter means operable to form first slits in an elongated strip of material at substantially uniform intervals along the length thereof, and second cutter means operable to sequentially form intermediate slits between said first slits, adjustable registering means for adjustably positioning said strip with respect to said second cutter means, and means for forming said strip and wrapping it around a tube.

2. A machine as set forth in claim 1 wherein said first cutter means consists of a pair of cooperating intermeshing cutter rolls, and said second cutter means consists of a pair of intermeshing cutter rolls.

3. A machine as set forth in claim 2 wherein a first roll cooperates with a second roll to provide said first cutter means and said first roll cooperates with a third roll to provide said second cutter means.

4. A machine as set forth in claim 3 wherein said rolls are each provided with axially spaced cutting teeth operable to simultaneously cut slits extending from opposite edges of a strip.

5. A machine as set forth in claim 4 wherein the axial spacing between the teeth formed on said third roll is different from the axial spacing of the teeth formed on said first and second rolls.

first, second,third and fourth cutting stations,and means to feed strips from said first cutting station to said second cutting station and from said third cutting station to said fourth cutting station 

1. A machine for forming spine fins for heat exchanger tubing or the like comprising first cutter means operable to form first slits in an elongated strip of material at substantially uniform intervals along the length thereof, and second cutter means operable to sequentially form intermediate slits between said first slits, adjustable registering means for adjustably positioning said strip with respect to said second cutter means, and means for forming said strip and wrapping it around a tube.
 2. A machine as set forth in claim 1 wherein said first cutter means consists of a pair of cooperating intermeshing cutter rolls, and said second cutter means consists of a pair of intermeshing cutter rolls.
 3. A machine as set forth in claim 2 wherein a first roll cooperates with a second roll to provide said first cutter means and said first roll cooperates with a third roll to provide said second cutter means.
 4. A machine as set forth in claim 3 wherein said rolls are each provided with axially spaced cutting teeth operable to simultaneously cut slits extending from opposite edges of a strip.
 5. A machine as set forth in claim 4 wherein the axial spacing between the teeth formed on said third roll is different from the axial spacing of the teeth formed on said first and second rolls.
 6. A machine for simultaneously forming a plurality of spine fins for heat exchanger tubing or the like comprising a first cutter roll, second, third, fourth and fifth rolls intermeshing with said first roll at peripherally spaced locations therearound and cooperating to form first, second,third and fourth cutting stations,and means to feed strips from said first cutting station to said second cutting station and from said third cutting station to said fourth cutting station. 